Means for retaining the internal tool, hereinafter called mandrel, are present in retained mandrel longitudinal weldless tube rolling mills.
Weldless tube rolling mills generally comprise one or more motors controlling respective pinions which, in turn, engage a rack which moves forwards and backwards. Such rack is generally supported by wheels or other guiding systems, e.g. runners or the like. A mandrel holder head is rigidly connected to the rack in which the tail shank of the mandrel is accommodated.
Motors retain mandrel feed and allow feed at a speed, called retained speed, chosen according to technological needs.
During the normal rolling cycle, at each subsequent rolling run, the mandrel is replaced with a new mandrel by means of automatic systems, normally of the rotating arm type. Such systems lift the mandrel to be replaced once it has performed its function and the respective shank integral with it, from the mandrel holder head with motion essentially directed from the bottom upwards. Such automatic systems lower a new mandrel along with the shank replacing the first with a reversed motion directed from the top downwards into the mandrel holder head.
The retaining function of the shank in the mandrel holder head is achieved by means of an essentially “U”-shaped device which defines a groove in which an undercut is made in which the shank is arranged by clamping. This traditional equipment is generally called a “guillotine”. The guillotine and the mandrel holder head are shaped so that the shank cannot be extracted with axial movement along the axis of the mandrel. A device of the prior art of this type is shown in FIG. 1 in section taken along an axial plane.
For accidental reasons, occasionally an unexpected interruption may occur and the rolling operation may not be completed due to causes of various type; consequently the rolling mill may stop with the machined tube still inside.
In such a situation, the mandrel which is still partially within the tube would in most cases be clenched by the tube itself and rigidly connected to the mandrel holder head. In such a case, resuming rolling mill operation would cause difficulties and delays, causing production downtime and hold-ups which have chain-effect repercussions on the rolling line.
An even more negative situation occurs in the case of severe jamming with the formation of unrolled material in excess in the spaces between cages, because the radial shift of the mandrel shank (5) to release the mandrel holder head (1) is essentially impossible, as there is no space for radial movements in transversal direction of the mandrel axis between mandrel holder head and shank.
Therefore a need is felt to make a mandrel holder head with release device which is very versatile in use and allows to overcome the aforesaid drawbacks.